Built-up edge effects on process outputs of titanium alloy micro milling

ContentslistsavailableatScienceDirect

Precision

Engineering

j ou rn a l h om epa g e :w w w . e l s e v i e r . c o m / l o c a t e / p r e c i s i o n

Built-up

edge

effects

on

process

outputs

of

titanium

alloy

micro

milling

Samad

Nadimi

Bavil

Oliaei

_,

_Yigit

_Karpat

a_{BilkentUniversity,DepartmentofMechanicalEngineering,MicroSystemDesignandManufacturingCenter,Bilkent,Ankara,Turkey} b_{BilkentUniversity,DepartmentofIndustrialEngineering,Bilkent,Ankara,Turkey}

c_{UNAM–InstituteofMaterialsScienceandNanotechnology,Turkey}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received28October2016

Receivedinrevisedform23January2017 Accepted22February2017

Availableonline6March2017

Keywords: Micromilling Microtools Built-upedge Titaniumalloy

a

b

s

t

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c

t

Built-upedge(BUE)isgenerallyknowntocausesurfacefinishproblemsinthemicromillingprocess. ThelooseparticlesfromtheBUEmaybedepositedonthemachinedsurface,causingsurfaceroughness toincrease.Ontheotherhand,astableBUEformationmayprotectthetoolfromrapidtoolwear,which hinderstheproductivityofthemicromillingprocess.Despiteitscommonpresenceinpractice,the influ-enceofBUEontheprocessoutputsofmicromillinghasnotbeenstudiedindetail.Thispaperinvestigates therelationshipbetweenBUEformationandprocessoutputsinmicromillingoftitaniumalloyTi6Al4V usinganexperimentalapproach.Microendmillsusedinthisstudyarefabricatedtohaveasinglestraight edgeusingwireelectricaldischargemachining.Aninitialexperimentaleffortwasconductedtostudythe relationshipbetweenmicrocuttingtoolgeometry,surfaceroughness,andmicromillingprocessforces andhenceconditionstoformstableBUEonthetooltiphavebeenidentified.Theinfluenceofmicro millingprocessconditionsonBUEsize,andtheircombinedeffectonforces,surfaceroughness,andburr formationisinvestigated.Long-termmicromillingexperimentwasperformedtoobservetheprotective effectofBUEontoollife.TheresultsshowthattailoredmicrocuttingtoolshavingstableBUEcanbe designedtomachinetitaniumalloyswithlongtoollifewithacceptablesurfacequality.

©2017ElsevierInc.Allrightsreserved.

1. Introduction

Micromillingoffershighflexibilityintermsofitsabilityto cre-atethree-dimensionalsurfacesmadefromavarietyofengineering materials.For example,micromillingis a commonlyused pro-cesstoproducemicromolds,whichareusedinmassproduction ofmicrocomponents[1,2].Thematerialremovalinmicromilling isrealizedbyusingmicroendmills,whichhavedefinedcutting geometries.Themicroendmillshavediameterslessthan1mm. Theinfluenceofmicroendmilldiameterontheprocessoutputs becomessignificantas thetooldiameterdecreases.Thecutting edgegeometryandsurfacequalityofthemicrotool,togetherwith theworkmaterialproperties,haveadirectinfluenceonthe qual-ityofthemanufacturedparts[3].Smalldiameters ofmicroend millslimitthemaximumcuttingspeedduringtheprocess.In addi-tion,feedvalueslowerthanthecuttingedgeradiusresultsinrapid roundingofthecuttingtooledge.Whenductilematerialssuchas

∗ Correspondingauthorat:BilkentUniversity,DepartmentofIndustrial Engineer-ing,Bilkent,Ankara,Turkey.

E-mailaddress:[email protected](Y.Karpat).

steel,aluminum,andtitaniumalloysaremachined,built-upedge (BUE)isobservedonthecuttingedgesanditaffectstheprocess out-putsandespeciallythesurfaceroughness.Anunderstandingofthe interplaybetweentoolwear,built-upedge,andsurfacequalityfor agiventool-workmaterialpairiscrucialforthesuccessful applica-tionofthemicromillingprocess.Theworkmaterialisselectedas titaniumalloyTi6Al4Vduetoitswidespreaduseinpractice[4–6]. TheinfluenceofBUEonmachininghasbeenconsideredmainly formacroscalemachiningprocesses[7–9].However,theinfluence ofBUEonthemicromillingprocesshasnotbeenstudiedindetail. ThepsontiandÖzel[10]observedBUEformationinmicromilling oftitaniumalloyTi6AL4V.Recently,Kovvurietal.[11]andWanget al.[12]studiedtheinfluenceofBUEwhilemachining316Lstainless steelandreportedthatBUEismainlyresponsibleforsurface rough-nessdeteriorationinthefinishmicromillingprocess.Theyshowed thatwhenBUEisnotpresent,theoreticalsurfaceroughnessmodels yieldacceptablepredictions.Ucunetal.[13]andAslantasetal.[14] bothstudiedthefinishmicromillingoperationandobservedthat coatedtoolsminimizeBUEandhelpimprovesurfaceroughness.

BUE affectsthefrictionconditions atthetool-chipand tool-workpieceinterfacesbyactinglikeacuttingedgesothatthecutting toolmaterialisnolongerincontactwiththechipandthemachined http://dx.doi.org/10.1016/j.precisioneng.2017.02.019

306 S.N.B.Oliaei,Y.Karpat/PrecisionEngineering49(2017)305–315

Fig.1. (a)Geometryofthedesignedsingleedgecuttingtool,(b)Designparametersofthetool.

surface.IwataandUeda[15]studiedmachiningoflowcarbonsteel andobservedthatfracturebehavioroftheworkmaterialaffects BUEformation and itsadhesiontothetool.They reportedthat toolraketemperaturebetween350and500◦Cprovidedthe nec-essaryconditionsforBUEtoadheretothecuttingtoolsurface.The influenceofrakefacetemperatureontheadherentlayerwasalso observedbyMillsetal.[16]whilemachiningcalciumdioxidelow sulphurcontentausteniticstainlesssteel.Kümmeletal.[17,18] cre-ateddimplesonthetoolsurfacetopromoteBUEformationduring macroscaleturningoperation.Thedimplesonthecuttingtool sur-faceincreaseBUEadhesiononthecuttingtool,henceimproving thetoollife.OliaeiandKarpat[19]fabricatedmicrocuttingtools usingwire electrical discharge machining,which creates micro scalecratersonthesurfaceofthetool,whichwasalsoshownto pro-moteBUEadhesionduringmachining.TheprotectiveeffectofBUE wasshownformicroturningprocess.Inthisstudy,thisapproachis carriedoutduringmicromillingoftitaniumalloyTi6Al4Vby fabri-catingmicrocuttingtoolsusingwireelectricaldischargemachining (WEDM).TheinfluenceofBUEontheprocessoutputsis investi-gated.Theresearchquestioniswhethertooldesignparametersand machiningconditionscanbeadjustedtoobtainastableBUEthat protectsthecuttingedge.Thismaybeespeciallyusefultoincrease materialremovalrateduringmicromillingoperation.

Varioustechniqueshavebeenusedtofabricatemicroendmills intheliterature[20,21].Endmillsfabricatedviaelectricaldischarge machining(EDM)havebeenshowntoworkeffectivelyonmetal alloysandpolycrystallinediamond[22–24].Thesurfaceintegrity andcuttingedge radiusaretwo importantissues. Studieshave shownthattailoredmicroendmillsdesignedforspecific machin-ingcasesyieldcomparableperformancecomparedtoconventional microendmills[25].Comparedtoconventionalmicroendmills, whichareproducedthroughgrindingprocesstohavehelicalflute geometry,thesetoolsusuallyhavestraightedges,whichimproves thestiffnessbutlimitsthechipevacuation.Theuseofstraightedges canbejustifiedbyconsideringthelowdepthofcutvaluesinmicro milling.

Inthisstudy,asinglecuttingedgemicroendmillhasbeen fab-ricatedusingwireelectricaldischargemachining.Theinfluenceof microendmillsurfacequalityanddesignparametersonthemicro millingprocesshasbeeninvestigated.AtooldesignforstableBUE formationwasselected.TheeffectofBUEonthemicromilling pro-cessoutputssuchassurfaceroughnessandburrformationwas investigatedforthesetgeometry.

Fig.2.(a)WEDMsetupusedformicroendmillsfabrication,(b)Schematic repre-sentationofmicroendmillfabricationprocess,(c)FabricatedsingleedgeWCmicro endmills.

2. Singleedgemicroendmilldesignanditsfabrication Anovelsingleedgecuttingtool geometryhasbeendesigned byconsideringtheproblemsassociatedwithtoolrunoutinmicro

Fig.3. (a)SEMimageofaWEDMedsurface,(b)EDSanalysisofWEDMedsurface.

Fig.4. 3Dtopographyandtopviewofthecuttingtools:(a)roughWEDMedtool,(b)finishWEDMedtool.

milling.Inaddition,a single-edgecuttingtool providesa lower toothpassingfrequency,whichhelpsconductexperimentsunder astablemachiningprocess.Thesolidmodeloftheproposed cut-tingtoolgeometryisdepictedinFig.1a.Tooldesignparameters canbeseeninFig.1b.Thelengthofcuttingedge,bottomandside clearanceangles,necktaperangleandtransitionradiusare con-sideredasmicroendmilldesignparameters.Thecuttingtoolhas astraightcuttingedge,whereeliminationofhelicalflutescan fur-therstrengthenthemicroendmill.Thelowdepthofcutvalues usedinmicromillingfurtherjustifyhavingstraightcuttingedges inthedesignedtools.

WEDMprocessisusedtofabricatemicroendmillsusingSodick AP250LhighprecisionWEDMmachinewithabrasswireof0.1mm diameterandoilasdielectricfluid.Ultra-finegraintungstencarbide rods(grainsize<0.7␮m)of4mmdiameterareusedformicroend

millfabrication.Tungstencarbiderodsaremountedontheindexer oftheWEDMmachineasshowninFig.2awitharunoutoflessthan 1␮m.Thetoolsarefabricatedintwosteps.Firstly,opencontour machiningwasperformedwithbottomclearanceangleincluded, thenthetoolisrotatedbasedonthedesignedsideclearanceangle, andanotheropencontourmachiningwasperformed.Depending ontherequiredsurfacefinish,multi-passWEDMwasperformed withdifferentrough,semi-finish,andfinishWEDMpasses.A care-fulselectionofWEDMparametersmadeitpossibletohaveafull controlonthesurfaceroughness,dimensionalaccuracyandedge radiusofthefabricatedmicroendmills.Fig.2bschematically illus-tratestheprocessofmicroendmillfabricationsteps.Fig.2cshows thefabricatedmicroendmillswithalengthofcutof800␮m, tran-sitionradiusof1.8mm,necktaperangleof90◦andbottomandside clearanceangleof7◦.

308 S.N.B.Oliaei,Y.Karpat/PrecisionEngineering49(2017)305–315

Fig.5. (a)Experimentalsetup,(b)Microstructureofthetitaniumworkpieceusedinthisstudy,(c)Schematicrepresentationofmicromillingexperiments.

EDMsurfaceisobtainedasaresultofcratersinducedbyaseries ofsuccessiverandomsparksontheworkpiece.Thesizeanddepth ofeachindividualcratertogetherwiththeoverlapbetween differ-entcratersdeterminethefinalmorphologyoftheEDMedsurface. Usinghighsparkenergiesresultinlargeanddeepcraters,and con-sequentlyaroughsurfaceisobtained.Sparkswithlowerenergies resultinsmallcratersandasaresultabettersurfacefinishcanbe achieved.Fig.3(a)illustratestheSEMimageofthesurfaceobtained afterWEDMprocess.Energy-dispersiveX-rayspectroscopy(EDS) analysisofthesurfaceisshowninFig.3(b).Thecompositionof thesurfaceismeasuredtobethesameasbulktungstencarbide material.

Thesurfaceroughnessisknowntohaveasignificantinfluence ontheperformanceofmicroendmillsandmicromachiningprocess outputs.Inordertoanalyzetheeffectofsurfaceroughnessobtained duringWEDMprocessonthemachiningperformanceofthemicro endmills,toolswithdifferentsurfaceroughnesswerefabricated. AfteradesignofexperimentsapproachonWEDMprocess param-eters,thebestsurfaceroughnessvaluewasobtainedas0.15␮m. Byapplyingadifferentsetofprocessparameters,asurface

rough-nessvalueof0.6␮mwasalsoobtained. Thesemicro toolswere fabricatedwithtwodifferentclearanceanglesat7◦and14◦. Differ-entclearanceangleandsurfaceroughnessvaluesresultindifferent cuttingedgeradiionthefabricatedmicroendmill.Another pur-poseofvaryingclearanceangleistochangethecuttingmechanics (strains,stresses,andtemperatures)atthetool-workpiece inter-face asmentioned in theprevious section.Fig. 4illustrates 3D topographyandtopviewofmicroendmillswherethedifference insurfaceroughnessandedgequalityofmicroendmillsare visi-ble.Table1summarizesthespecificationsoffabricatedmicroend mills.

3. Preliminarymicromillingexperimentsandobservations Inordertoanalyzetheeffectoftoolconditions(surfacequality, clearanceangleandedgeradius)ontheperformanceofmicroend mills,aseriesoffullimmersionmicromillingexperiments(slot micromilling)wasconductedonTi6Al4Vworkmaterialusinga DMGHSC55millingmachineequippedwithahighspeedspindle NSKHES510(Fig.5a).Theworkmaterialhasalamellar

microstruc-Table1

Specificationsofthefabricatedtailoredsingleedgemicroendmills.

Tool ClearanceAngle (◦) SurfaceRoughness Sa(␮m) EdgeRadius (␮m) ToolDiameter (␮m) Lengthofcut (␮m) Neckangle (◦) 1 7 0.15 2–3 390 200 90 2 7 0.6 4–5 3 14 0.15 1.5–2.5 4 14 0.6 4–5

Fig.6. RMSoftheresultantforce:(a)Conventionalmicroendmill,(b)FinishWEDMed-CA=14◦_{,(c)FinishWEDMed-CA=7}◦_{,(d)RoughWEDMed-CA=7}◦_.

turethathasbeenshowntobefavorableformicromillinginthe literature[26](Fig.5b).Theexperimentswereperformedatfeed pertoothvaluesof 0.6,0.8,1,2,and 4␮m/tooth,whilespindle speed and depth of cut were keptconstant at 28,000rpm and 30␮m, respectively.The depthofcut is between5 and10% of thetooldiameterasusedinpractice.Nocoolantwasusedduring theexperiments.Fig.5ashowstheexperimentalsetupformicro millingtests.Forcomparisonpurposes,a commercialmicroend millwithhelicalgeometryand0.4mmdiameterwasalsousedin

theexperiments.Theup-sharptoolhasacuttingedgeradiusof 2␮m.MachiningforcesweremeasuredusingKistlerminiforce dynamometer(9256C1,max250N).

Duringmicromillingexperiments,amethodologywasfollowed whichallowsforlongtermtestingofmicroendmills.Experiments startwithslotmillingoperationatdifferentfeedvaluesand follow-ingcompletionoftheslotmillingtests,toolswereusedincircular pocketmillingoperationassummarizedinTable2.After complet-ingthecircularpocketoperations,toolswereusedinslotmilling

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Fig.7. (a)Edgeconditionaftermicromilling,(b)MeasurementofaverageBUEheightby3Dlaserscanningmicroscope,(c)SEMimageoftheBUEformedinafinish WEDMed-CA=7◦.

Table2

ExperimentalConditions.

CuttingTools CuttingSpeed AxialDepthofCut Feedrate(um/tooth)

ConventionalMicroEndMill,Tools1,2,3,4 28,000 30 0.6,0.8,1,2,4

operationasbeforeandmachiningforcesweremeasuredagain. Thepurposeofcircularmillingoperationistoextendthe machin-ingtimesothatissuesliketoolwearandbuilt-upedgeformation canbeobserved.Fig.5bexplainstheexperimentalmethodology followedinthisstudy.

Fig. 6 shows the root mean square (RMS) of the resultant forcefor each milling case. Theresultant forceis calculated as



Fx2+Fy2+Fz2.Microendmillfabricatedtohavelargesurface

roughnessandclearanceangleof14◦wasobservedtobreakatthe beginningofthetest,sonoresultsarereportedforthattool.This prematurebreakagemaybeattributedtotheweakeningeffectof bothlargeclearanceangleandlargercratersduetohigherspark energiesappliedintoolfabrication.Asexpected,theRMSvalueof theresultantforceincreasebetweenfirstandthirdexperiments. Themagnitudeofresultantforcesforconventionalendmilland fabricatedendmillshavinglowsurfaceroughnesswith7◦and14◦ clearanceanglesareclosetoeachother.Whilethereisa signifi-cantincreaseinresultantforcesbetweenfirstandthirdslotmilling operationsfor the conventional micro end mill,theamount of forceincreaseinfabricatedmicroendmillsaresmaller.Fabricated microendmillwith7◦clearanceangleseemstobethemost favor-ableconsideringlargestfeedvalueof4␮m/tooth.Largerforcesare directlyrelatedtocuttingedgeradiusasseeninFig.6d.

Investigationofthecuttingedgesaftermicromilling experi-mentsshowsedgeroundingandbuilt-upedge(BUE)formation.

Fig.7ashowstheopticaland3Dlaserscanningmicroscopeimage ofthecuttingedgeoftheconventionaltoolaftermicromillingtests. Theedgeradiusofthemicroendmillhasbeenincreasedto6␮m fromaninitialradiusof2␮mandabuilt-upedgeformationtook place.Fig.7bshowstheBUEformationonthecuttingedgewith afabricatedtooloflowsurfaceroughnessand7◦clearanceangle. HavingastraightcuttingedgeleadstoalargerstableBUEformation infrontofthetoolcomparedtoaconventionaltoolwhichservesthe purposeofthisstudywheretheinfluenceofBUEonmicromilling isinvestigated.Themicroendmillwith7◦clearanceangleisused intheremainderofthestudy.

4. Investigationofmicromillingprocessoutputsinthe presenceofBUE

Thissectionaims tofurtherinvestigatetheeffectof BUE on micromillingprocessoutputssuchasmicro millingforces, sur-facequality,dimensionalaccuracyandburrformation.Thesame experimentalsetupusedin theprevioussection wasalsoused. Singleedgemicroendmillswithanominaldiameterof0.4mm diameterwith200␮mlengthofcutwereusedintheexperiments. Slotmicromillingexperimentswereperformedunderthe condi-tionssummarizedinTable3,whilefeedrateiskeptconstantat 4␮m/tooth.

(a)

(b)

Fig.8. (a)AverageBUEheight,(b)Normalizedresultantforce.

Table3

ExperimentalconditionsusedforBUEstudies.

Exp# SpindleSpeed(rpm) Depthofcut(␮m)

1 28,000 30 2 40 3 50 4 36,400 30 5 40 6 50

Thefeedselectioncorrespondstoroughmicromachiningcases wheremaximizingmaterialremovalrateisthegoal.Theprotective effectofBUEinthiscasewouldbethemostuseful.Foreach exper-imenttheaverageBUEheight(asdefinedinFig.7b),micromilling forces,surface roughness,and burrparameters weremeasured. TheaverageBUElengthismeasuredbylaserscanningmicroscope (KeyenceVX-110)asshowninFig.8a.BUEheightincreaseswith increasingdepthofcutfrom30␮mto40␮m,butdecreaseswith increasingdepthofcutfrom40␮mto50␮m.Itmustbenotedthat themeasurementsarequiteclosetoeachotherbyconsideringthe geometryofBUEinFig.7b.Theinfluenceofincreasingspeedon averageBUEheightisalsonotsignificant.However,theinfluence ofcuttingspeedanddepthofcutontheresultantforcesare sig-nificant.Inordertoremovetheeffectofdepthofcutvariations duetoBUEformation,RMSoftheresultantforcesarenormalized withrespecttodepthofcutmeasurementsaftertheexperiments using3Dlaserscanningmicroscope.Thereseemstobeacorrelation betweenBUEheightandresultantforces,butitmustbenotedthat cuttingforcesalsoreflectthematerialresponse.Thetitaniumalloy

Ti6Al4Vusedintheexperimentshasalaminarmicrostructurewith 10and20␮mgrainsize.

Fig. 9 shows the areal surface roughness (arithmetic mean height, Sa) measurements corresponding to each experimental case.3DlasertopographyofthemicrochannelsareshowninFig.9a forexperiments4,5and6.Analysisofthesurfaceroughnessof theexperimentsrevealedthatabettersurfaceroughnesshasbeen achievedcorrespondingtothelargestBUEheightwhichalso cor-respondstolargestmachiningforces.Thiscanbemainlybecause oftheburnishingeffectoftheBUEonthesurface.Similarresults were also observed in Oliaei and Karpat [19] in micro turning experiments.Ourexperimentalresultsarecomparabletosurface roughnessvaluesreportedinWangetal.[12]wherethefocuswas finishmicromillingexperiments.Itmeansthatcomparableresults canbeobtainedintermsofsurfaceroughnesswiththetailored tools.AstheBUEsizegetslarger,itislikelythatsomeloosebits willbesmearedtothebottomsurfaceofthemicrochannelwhich isexpectedtohinderthesurfacequality.

The final issue considered is the burr formation. Fig. 10a illustratesSEM imagesoftheburrs formedunderexperimental conditionsofTable3.SEMisusedtomeasureburrwidthanda lasermicroscopeis usedtomeasureburrheight.Themeasured burrheightandwidthforeachcuttingtoolareshowninFig.10b. Depthofcutisthemostinfluentialfactorinburrformation.The burrheightandwidthincreasewithincreasingdepthofcut.

ItisimportanttonotethatBUEformationatthecuttingedge affectsthewidthanddepthofthemicrochannel.When conven-tional micro end mills are used, which comes in standardized diameters, BUE formation hinders dimensional control during machining.However,whentailoredtoolsareused,tooldiameter

312 S.N.B.Oliaei,Y.Karpat/PrecisionEngineering49(2017)305–315

Fig.9.(a)3Dsurfacetopographyofthemachinedmicrochannels,(b)Arithmeticmeanheight(Sa).

Table4

Measureddepthandwidthofmicrochannels.

Experiment# DesiredMicrochannelDepth(␮m) MeasuredMicrochannelDepth(␮m) MeasuredMicrochannelWidth(␮m)

1 30 31 394 2 40 39 392 3 50 52 389 4 30 33 383 5 40 42 386 6 50 48 391

canbeadjustedbasedontheBUEformationtocontroldimensional tolerances.Therefore,itisimportanttohavepredictiveabilityon BUEsizeasafunctionofprocessparameters.Table4showsthe measuredmicrochannelwidthanddepthvaluesforeach experi-ment(Fig.11).

5. InvestigatingtheprotectiveeffectofBUEduringmicro milling

Inordertoanalyzetheprotectiveeffectofbuilt-upedge for-mationontool lifeofthefabricatedmicro endmills,longterm micromillingexperimentshavebeendone.For thispurpose80 microchannelswithalengthof50mmhavebeenmachinedata spindlespeedof28000rpm,feedrateof4␮m/toothandadepthof cutof50␮m.ItcorrespondstoExp#3inTable3.Themachining processhasbeeninterruptedaftermachiningeach20 microchan-nels, and tool condition is monitored using 3D laser scanning microscope.Fig.12illustratestheSEMimageoftheBUEformed atthe80thmicrochannel.

For each microchannel cutting forces are also recorded. Fig.13(a–d)illustratesthemeasuredcuttingforcesforthefirst,

second,40thand 80thmicrochannel,respectively.Betweenthe firstandsecondmicrochannels,thereisasignificantincreasein y-directionforceswhiletheforcesinxandzdirectionsare sta-ble.Thisincreaseisbelievedtoberelatedtoedgeroundingofthe cuttingedge,whichaffectsthemechanicsofthecuttingprocess. Increasingtheedgeradiuscreatedsuitableconditionsofmaterial accumulationinfrontofthetool.WiththestableBUEformationin place,thecuttingforcesalmostremainatthesamevaluethrough 80thmicrochannels.

Attheendoflongtermexperiments,togainan understand-ingaboutthepossibilityofchemical reactionbetweentool and work,BUEhasbeenremovedfromthecuttingtoolusinga clean-ingprocess.AnEDSanalysiswasperformedinalocationexactly underneaththeremovedBUE.TheEDSanalysisresultsareshownin Fig.14.EDSanalysisofthebulktoolmaterialisshowninFig.14(a). ThecobaltcontentofthetoolmaterialunderneathBUEhasbeen decreasedfrom11.6wt\%toabout8wt\%andthetungsten con-tenthasbeendecreasedfrom88%to86%.Thisdecreasehasbeen explained byHartung and Kramer[27] asthe formationof TiC layeratthetoolchipinterfacewhichwasreplenishedbythe car-bonatomsremovedfromtheWCgrainsonthetool.Theresults

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Fig.11. MicrochannelofExp.#6.(a)3Dimage,(b)MicrochannelProfile.Aheight magnificationof200%isused.

obtainedinthissectionareinagreementswiththeresultsof Oli-aeiandKarpat[19].AstableBUEwasshowntoprotectthecutting edgeinmicroturningprocess.Thesameprotectiveeffectisalso obtainedinmicromillingprocessusingtailoredmicroendmills.

Fig.12. SEMimageofBUEaftermachining80microchannels.

6. Conclusions

TheinfluenceofBUEontheprocessoutputsinmicromilling hasbeenstudiedusingatailoredsingleedgemicroendmill.The resultscanbesummarizedasfollows:

• Thesurfaceroughnessofthemicroendmillfabricatedwithwire EDMisanimportantfactoronthesuccessoftheprocess.

Fig.14.EDSanalysisof(a)bulktoolmaterial,(b)UnderneathoftheBUE.

• Amicroendmillwithlowclearanceangleyieldedthemost sta-bleconditioninBUEformation.Theperformanceofthetailored microendmillisobservedtobeacceptable.

• Ithasbeenobservedthat,largerBUEsizesresultedinlarger resul-tantforces.SurfaceroughnessimprovedwithincreasedBUEsize. ItmustbenotedthatalargeunstableBUEwoulddeterioratethe surfacefinish.Theselectionoffeedanddepthofcutforagiven workmaterialisanimportantconsideration.

• Increasing cutting speed did not improve surface roughness undertheexperimentalconditionsconsideredinthisstudy. • ThereisnocorrelationbetweenBUEandburrparameters.Large

forcesyieldedlargerburrs.

• ObtainingastableBUEduringmachininghelpsincreasethetool life,whichisanimportantissueinroughingoperationsespecially inmicromoldmaking.

• TheabilitytopredictandcontrolBUEsize,togetherwithtailored tooldesign,maybebeneficialinmicromillingpractice.

Acknowledgements

Theauthors would like tothank TheScientific and Techno-logicalResearchCouncilofTurkey(TÜB˙ITAK-110M660,National YoungResearcherCareerDevelopmentProgram)andState Plan-ningOrganization of Turkey(HAMIT-Micro System Design and ManufacturingResearchCenter).

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